I'm not quite sure anyone other than us knows how to actually calculate mpg effectively. I'm always right around what you're posting for overhead vs hand calculation...

For those of you who don't know, the most effective way is to fill up, reset the trip, drive your regular routes, fill up again, take the mileage driven in that time and divide it by the amount of gas the second fill up took. Neither fill up should be topped off, preferably use the same pump at the same station to ensure accuracy between pump error, and ensure you have the correct speedometer gear for your tire size. If you stray from this, you're not going to get accurate calculations.

Only thing extra I'd suggest is doing that same process over several fill ups. The more readings you do, the more accurage an average you will get. Bigger sample = more reliable data.

Maybe I lucked out having 235 vs 225 tires giving the offset for good readings? The avg is pretty much spot on(+/-.3) when I do my own checks for my overhead O_o I do exactly as you said(that's how I was taught and reliably check it, plus my math teacher drilled averages into us for 2 weeks one year so there's no way I could forget it).

Only thing extra I'd suggest is doing that same process over several fill ups. The more readings you do, the more accurage an average you will get. Bigger sample = more reliable data.

Maybe I lucked out having 235 vs 225 tires giving the offset for good readings? The avg is pretty much spot on(+/-.3) when I do my own checks for my overhead O_o I do exactly as you said(that's how I was taught and reliably check it, plus my math teacher drilled averages into us for 2 weeks one year so there's no way I could forget it).

Accuracy of the overhead seems to be luck of the draw. Because of my bigger than stock fuel injectors, mine will always read about 10% higher than it otherwise would have, but it's off by more than that most of the time.

Accuracy of the overhead seems to be luck of the draw. Because of my bigger than stock fuel injectors, mine will always read about 10% higher than it otherwise would have, but it's off by more than that most of the time.

I guess that being accurate makes up for the VIC constantly having "srvc 4wd switch" beeping nonstop for a couple years till it died recently

Lol. Just wait till I post pics. I had a 93 back in 98 that wasn't this clean.

Join the club lol yeah I love my 5 speed zj one good think about mine is I stole it for 500 bucks and have been driving it daily for a few years now I actually lost track how long I had it I think back in 09 lmao mine sadly is not rust free but at least I don't have to worry about scratching or damaging it lol.

Only thing extra I'd suggest is doing that same process over several fill ups. The more readings you do, the more accurage an average you will get. Bigger sample = more reliable data.

Maybe I lucked out having 235 vs 225 tires giving the offset for good readings? The avg is pretty much spot on(+/-.3) when I do my own checks for my overhead O_o I do exactly as you said(that's how I was taught and reliably check it, plus my math teacher drilled averages into us for 2 weeks one year so there's no way I could forget it).

Oh yeah, I'll agree with that. The more samples you have, the better. My running average, according to Fuelly, is 13.9 MPG. I've calculated a lot worse than that and also had Fuelly represent a lot lower than that. I've also had some really good tanks where I had 200 miles of highway driving that averaged quite high. To be honest, I'm surprised my Fuelly average is that high. That's tracked for over 10,000 miles as well so I'd imagine it's fairly accurate. About all of that is with my lift and maybe 5000 of it is with my 31s. All in all, I guess for what my ZJ has done to it, that's not too terrible for an average.

Did you do it by yourself or did you get help? I did mine by myself including the hitch. That was fun. I couldn't get anyone to help me out that day. A folding chair worked well to keep things balanced on one side while I managed to get one side loosely secured.

Hahah yep did this one by myself, held the skid up with a ratchet strap then used jack stands for the hitch. Pain the *** but I got er done

Funny enough, I've never had much error in my overhead. In the Laredo, it calculated a number that was off by almost exactly the amount the tires threw off the speedometer. And in the Orvis, it shows the same 11.1mpg I've hand-calculated.